Internal combustion engines may include water injection systems that inject water into a plurality of locations, including an intake manifold, upstream of engine cylinders, or directly into engine cylinders. Injecting water into the engine intake air may increase fuel economy and engine performance, as well as decrease engine emissions. When water is injected into the engine intake or cylinders, heat is transferred from the intake air and/or engine components to the water. This heat transfer leads to evaporation, which results in cooling. Injecting water into the intake air (e.g., in the intake manifold) lowers both the intake air temperature and a temperature of combustion at the engine cylinders. By cooling the intake air charge, a knock tendency may be decreased without enriching the combustion air-fuel ratio. This may also allow for a higher compression ratio, advanced ignition timing, and decreased exhaust temperature. As a result, fuel efficiency is increased. Additionally, greater volumetric efficiency may lead to increased torque. Furthermore, lowered combustion temperature with water injection may reduce NOx, while a more efficient fuel mixture may reduce carbon monoxide and hydrocarbon emissions.
As explained above, water may be injected into different locations, including the intake manifold, intake ports of engine cylinders, or directly into engine cylinders. The inventors herein have recognized that port and/or direct injection may increase a dilution effect of the injected water over manifold injection, thereby reducing engine pumping losses. Additionally, while direct and port injection may provide increased cooling to the engine cylinders and ports, intake manifold injection may increase cooling of the charge air without needing high pressure injectors and pumps. However, due to the lower temperature of the intake manifold, not all the water injected at the intake manifold atomizes properly. Condensed water from water injection may accumulate within the intake manifold and result in unstable combustion if ingested by the engine. Additionally, manifold water injection may result in uneven water distribution amongst cylinders coupled to the manifold. As a result, uneven cooling may be provided to the engine cylinders.
In one example, the issues described above may be addressed by a method for an engine including, in response to a request for water injection, selecting, based on engine operating conditions, a location for water injection from each of: an intake port of each cylinder, an intake manifold upstream of all engine cylinders, and directly into each cylinder; and injecting water at the selected location. In this way, water injection may be utilized both for increasing engine dilution to decrease pumping losses and provide increased charge air cooling to reduce engine knock and increase engine efficiency.
As one example, water may be injected at different locations under different engine load and/or engine speed conditions. For example, when engine load is less than a threshold, water may be injected at an intake port of each cylinder. In another example, when engine load is greater than a threshold, water may be injected at an intake manifold upstream of all engine cylinders. In yet another example, when engine load is greater than a threshold and water injection at the intake manifold reaches an upper threshold amount, water may be injected directly into the engine cylinders. Additionally, the amount of water injected may be adjusted based on an estimated portion of the amount of water that vaporized and an estimated portion of the amount of water that remained liquid following injection. In this way, water injection may be used to increase engine efficiency, including reducing pumping losses, reducing fuel consumption, reducing engine emissions, and reducing engine knock.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.